UV-Triggered Self-Healing of a Single Robust SiO₂ Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings

Abstract

UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO2 microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO2 precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO2 microcapsule via a combined interfacial/in situ polymerization. The single SiO2 microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO2 microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO2 microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen.

Effect of Urea-Formaldehyde-Coated Epoxy Microcapsule Modification on Gloss, Toughness and Chromatic Distortion of Acrylic Copolymers Waterborne Coating

“…At present, there are many modification methods for waterborne coatings, such as organosiloxane modification [9], polyurethane modification [10], nanomaterials modification [11] and microcapsules modification [12]. In particular, it was found that adding microcapsules to waterborne coatings can improve the water resistance, wear resistance and the healing properties of coatings [13], which had attracted wide attention [14].…”

Preparation and Optimization of Waterborne Acrylic Core Microcapsules for Waterborne Wood Coatings and Comparison with Epoxy Resin Core

“…Although its application in wood coatings is still in the development stage, it has great application prospects [ 4 , 5 , 6 ]. Self-healing technology, as a new effective way to suppress coating micro-cracks, has become a research hotspot in many application fields [ 7 , 8 , 9 ]. Functionalized and application-oriented microcapsules are added to the coating to improve the repair ratio of the coating while enhancing the coating performance [ 10 ].…”

Preparation of Shellac Resin Microcapsules Coated with Urea Formaldehyde Resin and Properties of Waterborne Paint Films for Tilia amurensis Rupr.

“…Therefore, the good fluidity, proper curing speed, and good compatibility with paint film substrate are the necessary conditions for selecting core materials [ 5 ]. Compared with the traditional repair technology, the key for microcapsule technology lies in its simple synthesis, low cost, and self-healing of materials without the aid of external conditions [ 6 ].…”